If you are using standard implicit joins PostgreSQL will be able to determine the join order for those joins automatically. This means that 8 explicit joins are implicitly planned. Let us take a look at the following configuration variable which can be found in nf: However, there are some subtle differences which are worth mentioning. If you happen to run a typical application there is no difference. Test=# explain SELECT * FROM a JOIN b ON (aid = bid) īasically the optimizer handles both queries the same way for MOST queries. Test=# explain SELECT * FROM a, b WHERE aid = bid If you look at the execution plan you will see that both plans are absolutely identical. It is merely a question of taste and style that is relevant here. Test=# SELECT * FROM a JOIN b ON (aid = bid) īoth syntax variations are identical. The alternative is to use an explicit join: In the FROM clause we only list the tables we want to join. In this the join actually happens in the WHERE-clause. Test=# SELECT * FROM a, b WHERE aid = bid The question people often ask is: What is the difference between an implicit and an explicit join? The answer is simply syntactic sugar. It consists of two tables containing a handful of rows which will be used for our little demo. Producing sample dataīefore we can get started we need to create some sample data: What are the differences between inner joins, outer joins, semi joins and so on? Let’s shed some light on them and see how inner and outer joins really work. Full join inner join left join outer join postgresql right joinĪ join is a concept in IT which is widely used and often referred to but rarely really understood.
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